Automatic volume control



i 1947- F. G. CRAWFORD ET'AL 2, ,9 3

AUTOMATIC VOLUME CONTROL Filed Aug. 5, 1944 INVENTORS.

H, 5 floss/150v.

Patented May 20, 1947 2,420,933 AUTOMATEC VOLUME CONTROL Frederick G.Crawford and Edgar A. Stroschein,

Oshkosh, Wis,

assignors to The Rudolph Wurlitzer Company, Chicago, 111;, a corporationApplication August 5, 1944, Serial No. 548,178

8 Claims.

This invention relates to an automatic volume control for a programamplifying circuit such as employed in phonographs, and particularlythose of the coin operated type, radio receiving sets, public addresssystems and the like.

The chief object of the invention is to automatically control the normalamplification of a program amplifier in accordance with the noiseintensity in the surroundings, room, etc., into which the amplifyingloud speaker discharges the program.

The invention eliminates loud volume nuisance which is generallyrecognized as a serious objection under varying conditions and in manylocations. With the present invention the program amplifier circuit isinitially set for proper volume to be heard in that location when thesurroundings are quiet. As noise varies, increases or decreases, theautomatic volume control causes the amplified volume to imperceptiblyincrease and decrease with the increase and decrease in surface noisevolume.

The control is of such sensitiveness that if the surface noise suddenlyceases, there is sub stantially no interim during which the programamplified volume is of blaring character, in other words, the element oftime lag between control registration and actuation is substantiallynegligible. It has been found that the change is so imperceptible to anaudience that until the actual change is called to its attention, norecognition of program volume variation is noted.

The principal object of the invention, therefore, consists in providingan amplifying circuit, such as in an electric phonograph, radio receiveror public address system and the like with an automatic volume controlsuch as to maintain a constant relation between the volume of amplifiedsound and surface noises.

One feature of the invention resides in the manual adjustment of asurface noise microphone, the program microphone, the lag and thebalancing potentiometers.

Another feature of the invention consists in interposing a filter anddelay circuit between the vsurface noise pick-up and amplificationcircuit, and the program amplification circuit.

A further feature of the invention resides in the inclusion of abalancing arrangement in series with one portion of the noise volumetransfer tube so that the program change will not affect the automaticvolume control.

Preferably the invention also contemplates the inclusion of a simple,automatic stop volume control, adjustable for any given maximum volumedesired and beyond which the program volume will not increaseautomatically regardless of any further increase in noise volume.

Other objects and features of the invention will be set forth more fullyh r i aft r- The full nature of the invention will be understood fromthe accompanying drawings and the following description and claims.

In the drawing, the figure is a-schematic wiring diagram of oneembodiment of the automatic volume control.

In the drawing, the upper portion represents generally the surface noisepick-up and amplification circuits, the lower portion represents theprogram pick-up and amplification circuits, while the intermediateportion comprises the connecting circuits which connect the aforesaidcircuits together for the purpose described, the said con nectingcircuits including a filter and delay circuit.

The schematic diagram, by way of eXampe only, has included thereinconventional designations for certain tubes as illustrated, the capacityand resistance values, and voltage values thereof. It is also to beunderstood that certain portions of the circuit illustrated may bemodified as desired or required, such as for example that immediatelyassociated with a phonograph amplifier.

In the diagram 5 indicates a noise microphone of the permanent magnettype which is associated with an input transformer I0 bridged by a noisevolume control potentiometer 62 having a manually adjustable tap 62connected to a grid l of the input tube l. The potentiometer is groundedby line 62 Cathode l is connected to resistor i3 which is grounded bythe line 52 Grid l is also connected to said resistor as shown. Theplate i of said tube is connected to capacity H by line H--. Line lifrom said capacity connects to grid 2 of the second stage microphoneamplifying tube 2. Resistor (ii is grounded at one end, and its otherend is connected to line li Condenser H is of a coupling characterbetween the first and second stages of the noise amplification system.

Tube 2 in addition to grid 2* includes the plate 2 and cathode 2 Thecoupling condenser i2 is connected by lines se and it to the plate 2* oftube 2 and grid 3 of the third, and herein the final stage amplifyingtube 3. Resistor it has one end grounded and the other end connected toline I2 Tube 3 also includes the plate 3, cathode 3 and a second grid 3Cathode 3 is connected to its resistor 22) and in multiple there r withis capacity 69, both being grounded remote from the cathode connection.

In like manner, cathode 2 of tube 2 is connected to resistor t5 and inmultiple therewith is capacity It, both being grounded remote from thecathode connection. 1

Tube 1 alsoincludes a grid if connected by line iii to the junction ofresistors 23 and 2d, the other terminal of the former being grounded andthe other terminal of the latter connecting to line H. The aforesaidjunction is connected to a grounded capacity 63.

Line H connects to a resistor M which is connected to line H and itsother end is connected to a grounded capacity 64, The line 7| capacity64 connection is connected to one terminal of resistor 25, the otherterminal being connected to line 72. Line 12 connects to one terminal ofresistor l7, the other terminal being connected to line [2 The junctionof line 72 and resistor 25 is connected to a grounded capacity 2%.

Tube 3 includes the second grid 3 connected to resistor 21. Plate 3 ofsaid tube is connected to resistor 22 by line 13 Line 73 from thisresistor has one branch 13 connected to line i2 as illustrated, and hasa second branch 13 leading to the push-pull arrangement, to whichreference will be had later.

Another line 74 connects to line l3 and capacity 36, and the latter isconnected to one plate 4 of diode tube 4. Resistor 27 has one terminalgrounded and the other connected to the connection between the capacity35 and plate 4 The aforesaid noise amplifier arrangement is a high gainamplifier of fair fidelity and the output from tube 3 is about one wattfor the specific example illustrated herein.

The cathode 4 of diode tube 4 is fed into a filter and delay circuit andfrom that into a tertiary grid of a multi-grid tube 5, which may be aphonograph microphone input tube.

The theory of operation is briefly that, as the volume of the surfacenoise increases, the microphone circuit (see top portion of the diagram)will introduce higher impulses into the circuit of tube 4, andaccordingly more positive voltage will be available for the saidtertiary grid of the input tube 5 which will raise the volume of theprogram amplifier proportionately.

Since the noise microphone 9 will pick up the program sounds, and theforegoing circuit will amplify same as well as the surface noises andthus try to control the phonograph input tube 5, provision is made tobalance out the music component, for if this were not done, thephonograph amplification would progressively increase to the maximumpossible volume and thus defeat the primary object of the invention.

Such compensation or balancing is attained as follows: Cathode 4 ofvolume control tube 4 is connected to the balancing potentiometer 3'! bya tap 37 This potentiometer is grounded at one end and its otherterminal is connected to the capacity 38, which is in turn connected toline 69, included in the push-pull portion of the program amplificationsystem. Specifically here-' in plate 6 of tube 6 is inductivelyconnected to the aforesaid line 69.

The filter and delay circuit aforesaid includes cathode 4 and plate 4 oftube 4. Line 15 from cathode 5 has positive potential while line 16 fromplate li has negative potential. Each line is connected to a groundedcapacity, 3! and 32 indicating such condensers for lines 15 and 16respectively. Each line similarly is connected to a resistor having oneterminal grounded, 33 and 34 indicating such resistors for lines 75 and76 respectively. Each line connects toanother resistor, such as resistor30 for line 15 and resistor 44 for line iii. The other ends of suchresistors connect to line 71. Bridging lines 15 and 75 is resistor 35.Preferably the values of resistors 30 and 44, capacities 3| and and 32and resistors 33 and 34 are equal.

Line 11 connects to one terminal of a potentiometer 28 having adjustabletap 28 In multiple therewith is grounded capacity 29. The other terminalof resistance 28 also is grounded. Tap 28 connects by line '18 to theaforesaid tertiary grid 5 of input tube 5 and thus the volume control ishere imposed upon the program amplification system.

Whenever it is desired to change the lag value of such control the tap28 is shifted. When line 78 applies positive voltage to grid '5, thereis a gain or increase in volume. When no voltage is applied, there is nochange and when the voltage is negative, there is a decrease in volume.A voltmeter may be included from line 18 to ground when desired, as forinitial adjustment purposes.

Reference will now be had more particularly to the program microphoneamplification system illustrated in the lower third portion of thediagram. Herein 79 indicates one terminal connected to capacity ll inturn connected to capacity 2 in multiple with the program volumepotentiometer 43 having adjustable tap 43 connected by line 99 to grid 5of input tube 5 aforesaid. Cathode 5 of this tube is connected toresistor 50 and grounded capacity 5!. The other terminal of resistor 59is herein connected to one terminal of resistor 52, the other terminalof which is grounded. A capacity 53 is in multiple with resistor 52.Potentiometer 43, capacities 42 and 53 and resistors 58 and 52 have acommon connection as illustrated.

Interposed between plate 5 and tertiary grid 5 of tube 5 is a grid 5 andinterposed between grids 5 and 5 thereof is grid 5 There grids 5' and 5have common connection to resistor 54, the other terminal thereof beinggrounded and in multiple with said resistor in capacity 55.

The plate 5 of input tube 5 is capacity connected to grid 6 of tube 6 bylines 45 and 45 and capacity 55. Tube 6 is a second stage amplificationtube having grid 6', plate 5 and cath- I ode 6. This cathode isconnected to its resistor 49, the other terminal of which is grounded.In multiple with resistor 49 is capacity 48. A resistor 41 is connectedat one end to line 45 and its opposite end is connected to the junctionbetween resistors 56 and 58. The other terminal of resistor '55 isconnected to the connection between resistor 54 and grids 5 and '5before mentioned. The junction of resistors 87, 56 and 58 connects togrounded capacity 57.

The plate 6 aforesaid, of second stage tube 6 is connected by line 8! tothe input side 82 of the input push-pull transformer 39. This winding isconnected by line 83 to the other terminal of resistor 58 and thejunction is connected to grounded capacity 59. The output side 84 of theinput transformer 39 includes a median tap 35 having, in the exampleillustrated, a negative voltage of 20 volts.

Line 86 connects one end of Winding 84 to grid 8 of the tube 8 havingcathode 8, plate 8 and another grid 8 Line 69 before mentioned connectsto the other end of winding 84, capacity 38 aforesaid and grid 1 of thetube 1 having cath ode 7, plate 7* and another grid 1 Plate 8 isconnected by line 8'! to one end of winding 83 of the output push-pulltransformer 49 having median tap 89. Line 30 connects the other end ofwinding 83 to plate 1 of tube 1. This output transformer has winding 9!as shown.

Cathode 7 and cathode 8 of tubes 1 and 8 are each-grounded as shown.Grids I and 8 of said tubes are connected together by line 88 which atone end connects to line 83 aforesaid and at its opposite end toresistor 60 having its other end connected to tap 89 and to line idthrough resistor 22 from the output side of the noise amplifying tub-e3. Terminal 92 also connects to the last mentioned junction and has apotential of three hundred positive volts in the example illustrated.

Whenever it is desired to include between the input and output tubes ofthe microphone and program circuits, more than a single stage ofamplification, same can readily be effected by inclusion of additionalamplification tubes in the manner well known at this time.

The following is the procedure for adjusting the invention for use. Thepotentiometer tap 62 (microphone control) is turned off. The tap 37 ofthe balance control is turned to one extreme position. Then the tap 43of the program input potentiometer control is adjusted for programinitial volume necessary for the minimum noise level present. The tap 62is then adjusted to about three-fourths of its available travel. With nonoise present, tap 31 is now adjusted to obtain the program volumepreviously obtained before the microphone control was shifted. Shiftingof tap 31 should be slow and cautious due to delay action. If differenttapers of volume regulation are required, the microphone control is setdifferently than as last suggested and the above procedure repeated.Control 28 is only utilized to adjust for different lags.

When properly adjusted, this invention balances out any program increaseincident to noise increase, and insures that the program will increaseand decrease only in accordance with surface noise increase and decreaserespectively.

For ideal conditions of operations, it appears advisable to have twomicrophones 9 placed parallel at remote points of maximum surface noise.Since such parallel microphone connections are well known, illustrationthereof is believed unnecessary.

It is to be noted that for tubes 2 and 6 the cathodes each may begrounded, or either grounded, or self-biased by the respective resistorsand bypass condensers, ll6 and it-43 respectively. Each is correct andthe circuit arrangement actually utilized is the one producing the bestresults.

Also relative to condenser 42, this is utilized to prevent stray radiofrequency waves from being picked up and allowed to cause sounds toemanate from the loud speaker. Alternative to that illustrated herein,condenser 42 may be grounded directly instead of through condenser 53and the latter would still be grounded and across resistor 52. Eithervariation is satisfactory for elimination of stray frequencies. Whennone are present, condenser 42 may be omitted.

The invention claimed is:

1. A sound volume control system including in combination a programamplifying circuit, a surface sound pick-up and amplifying circuit, andcircuit means inter-connecting the input of the first mentioned circuitto the output of the second mentioned circuit for automatically varyingthe program output volume only in accordance with surface soundvariation, and means for simultaneously balancing out of the effectedcontrol that increase in the surface sound volume due to program soundvolume increase.

2. In combination with a surface sound pickup and amplifying circuitincluding a microphone, an input transformer, a multi-grid tube, anamplifying tube and an output multi-grid tube, a program pick-up andamplifying circuit including a multi-grid input tube, an amplifyingtube, a pair of multi-grid multiple connected tubes having their platesconnected to an output push pull transformer and one grid connected tothe input push pull transformer, and a control circuit comprising adiode tube connected to the output stages of the output tubes of thefirst two circuits and also connected to a grid of the multi-grids ofthe input tube of the program circuit.

3. A sound volume control system including in combination a programamplifying circuit, a surface sound pick-up and amplifying circuit, andcircuit means inter-connecting the input of the first mentioned circuitto the output of the second mentioned circuit for automatically varyingthe program output volume only in accordance with surface soundvariation, the interconnecting circuit means including a filter anddelay arrangement.

4. A sound volume control system including in combination a programamplifying circuit, a surface sound pick-up and amplifying circuit, andcircuit means inter-connecting the input of the first mentioned circuitto the output of the second mentioned circuit for automatically varyingthe program output volume only in accordance with surface soundvariation, the interconnecting circuit means a filter and delayarrangement, and a manually adjustable "means for adjusting saidarrangement for predetermined lag.

5. A sound volume control system including in combination a programamplifying circuit, a surface sound pick-up and amplifying circuit, andcircuit means inter-connecting the input of the first mentioned circuitto the output of the second mentioned circuit for automatically varyingthe pro-gram output volume only in accordance with surface soundvariation, and means for simultaneously balancing out of the effectedcontrol that increase in surface sound volume due to program soundvolume increase, said last mentioned means including an adjustablepotentiometer capacity coupled to the output portion of the programamplifying circuit.

6. A system as defined by claim 2 wherein the surface sound pick-upcircuit includes an adjustable potentiometer.

7. A system as defined by claim 2 wherein the program circuit includesan adjustable potentiometer.

8. A system as defined by claim 2 wherein each circuit includes anadjustable potentiometer.

FREDERICK G. CRAWFORD. i EDGAR A. STROSCHEIN.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS Number Name Date 1,356,403 Pridham Oct. 19, 19201,733,232 Miessner Oct. 29, 1929 2,160,097 Weathers May 30, 19392,338,551 Stanko Jan. 4, 1944

